1. Field of the Invention
The present invention is related to quality assurance inspection of Pin Grid Array semiconductor packages, and specifically, to the detection of bent leads on a Pin Grid Array semiconductor package. The present invention improves overall inspection productivity by automating a conventionally manual process.
2. Discussion of the Related Art
In the manufacturing of integrated circuits, the semiconductor dies are placed inside packages. The package protects the die from damage, provides a thermally conductive path away from the die in order to dissipate heat, and provides electrical connectivity to other circuit elements. The electrical connections of the package are called leads. In a pin grid array, the leads are metal extensions (pins) which protrude downward from the underside of the package. The leads placed at points along a rectangular matrix (grid). In order to integrate the pin grid array into a circuit board, the package is inserted into a mating connector having a rectangular matrix of holes for receiving the leads of the pin grid array. The mating connector is either mounted on the circuit board or is formed in the circuit board itself.
Pin grid array packages are usually chosen for integrated circuits having a very large number of leads. Integrated circuits having fewer inputs and outputs can be contained in packages having leads only along the peripheral edges of the package, without having connections underneath. The large number of leads in the pin grid array package can require a large insertion force when installing the pin grid array into the mating connector.
In order to properly install the pin grid array, all the leads must exactly match up with the corresponding holes in the mating connector. If a lead is very slightly bent, that lead will require a greater force to insert into the mating connector. In this case, the process of installation will unbend the lead. However, if the lead is more severely bent, that lead may not install properly at all, but rather will not make contact with its mating hole. Installation of the severely bent lead will bend the lead even further, perhaps breaking it off, and preventing the proper installation of the pin grid array into the circuit board. Therefore, the inspection of the leads for bends is a necessary part of the final inspection of pin grid array integrated circuits prior to shipment.
Conventionally, the inspection for bent leads of pin grid array packages has been performed manually. This manual inspection is tedious as the inspector must strain her eyes to search for bent leads. Additionally, the conventional process of manual inspection for bent leads is unreliable and inspector dependent, resulting in human error and inconsistency. False positives and false negatives occur more frequently for less experienced and less skilled inspectors. A false positive is the incorrect identification of a pin grid array as having a bent lead, when in reality the pin grid array was not flawed, and therefore did not have any bent leads. A false negative is the incorrect identification of a pin grid array as being good, and thus having no bent leads, when in fact the pin grid array was flawed, and did have bent leads. False positives during lead inspection unnecessarily reduce the yield of the manufacturing process while false negatives result in the shipment to customers of flawed products.
Moreover, the conventional manual inspection for bent leads of pin grid arrays is more time-consuming for larger, more complex pin grid arrays having more leads. The time required for conventional manual inspection for bent leads of pin grid arrays is roughly proportional to the number of leads. This variable inspection time creates additional complications in scheduling the correct number of inspectors for the inspection workload.
As is apparent from the above discussion, a need exist for an automated process of inspection for bent leads which is not prone to human error and which requires only a constant amount of time for pin grid arrays of all complexities.